More than 1.5 million homes have been left blighted by botched cavity insulation work carried out to meet Government energy targets, experts say.

Properties across Britain have suffered dampness and mould, causing smells, crumbling plaster and stained walls. In some cases, the value of homes has plunged.

The Government scheme was meant to make homes more energy-efficient but some owners say their bills have increased since having the cavity wall insulation work done

The scheme, funded by a ‘green tax’ on household gas and electricity bills, was meant to cut emissions and reduce charges by making homes more energy-efficient.

But experts claim that many homes were simply not suitable for ‘retrofitting’ cavity wall insulation, while others were in parts of Britain where weather conditions should have precluded its use.

Some people have been left suicidal

Millions were persuaded to sign up to the scheme by the promise of cheaper bills from call-centre staff and door-to-door salesmen employed by energy firms obliged to meet Government targets.

A survey of 250,000 properties by thermal-imaging company IRT found the addition of cavity wall insulation to existing homes had failed to work in a quarter of cases and problems in half the homes it surveyed. Some owners even saw bills rise.

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With more than six million properties having had the treatment since 1995, this suggests that as many as 1.5 million are affected.

Campaigners claim some people are suicidal after their properties were left riddled with damp patches and mould as a result of botched fitting, which can take thousands of pounds to put right.

Among the victims are Helen Thomson, from Cornwall, whose farmhouse suffered such serious problems after cavity wall insulation was installed that £30,000 of repairs are needed.

Helen Thomson shows off the walls at her home in Cornwall which were left damp by cavity wall insulation

And Deborah Wassell, of Southampton, had her insulation removed after furniture went mouldy and her son suffered asthma attacks.

Pauline Saunders, who set up Cavity Wall Insulation Victims’ Alliance after problems at her home in Newport, South Wales, said: ‘We’ve been inundated with people whose homes have been ruined. It has got so bad for some that they have been left feeling suicidal.

'Even if half the findings of the study are true, more than a million people’s homes will have problems.’

Last month, Ministers published a report which admitted there were ‘too many poor-quality installations’ by companies which ‘do not have the skills required’.

Stephen Hodgson, of the Government-endorsed Property Care Association, said some homes were simply not suitable for the work as their design meant the insulation – which is pumped into walls via holes drilled into the exterior brickwork – acts as a ‘bridge’ for moisture to cross the cavity into the house.

He said: ‘Contractors were desperate to mop up vast sums of money made available by energy firms on the back of Government green targets.’

Under Government rules introduced in 1994, energy firms must help improve the efficiency of their customers’ homes, with costs added as a levy to all household fuel bills. The cost is around four per cent on top of an energy bill – equivalent to £47 per year on average.

Experts claim that many homes were simply not suitable for ‘retrofitting’ cavity wall insulation

Many householders told The Mail on Sunday of difficulties getting compensation from the Cavity Insulation Guarantee Agency (CIGA), which was set up to pay for repairs caused by botched work. Experts also say its £18 million fund is not enough but the agency’s chief executive Nigel Donohue insisted: ‘Customer satisfaction rates are up.’

Neil Marshall, chief executive of the National Insulation Association, disputed IRT’s findings. He said: ‘These figures are widely inaccurate as thermal cameras in isolation are ill-equipped to assess the effectiveness of cavity wall insulation.’

However, he admitted that at least 13,000 of the six million CIGA-guaranteed homes had reported problems.

An Energy Department spokesman said that Government programmes required companies installing insulation to be accredited and to provide a guarantee.

'Our house is ruined ... we are in a living hell'

Brendan O’Brien, from Plymouth, fears his semi-detached house will fall down around him, his partner and their three children because the walls are so waterlogged after cavity wall insulation was installed in 2004.

‘We are in a living hell,’ said the 44-year-old. ‘The house has become so waterlogged it has cracked the gable end of the house. The front window is about to fall out.

‘There is serious structural damage and there is no point in decorating or putting down carpets because it all gets ruined in the damp. A worker came out to look at it. He drilled into the wall and water was pouring out. It has collected like a sponge between the walls.’

Helen Thomson, 56, from Bude, Cornwall, needs £30,000 of repairs to her five-bedroom farmhouse due to horrific problems.

Her late mother Patricia, who also lived at the property, was taken in by a cold-calling salesman who convinced her the house was a perfect fit for the work in 2009. But insulation should never have been carried out at the property – the exposed location of the home, on a hill in a rainy rural area, meant rainwater soaked into the new insulation, leading to a chronic damp problem.

Mrs Thomson’s daughter Ella Gillies, 30, said: ‘My mother has been hospitalised twice due to lung conditions and the doctor told me he thinks it was due to mould caused by the insulation. It has ruined her life.

‘The house should never have had insulation. It was a beautiful five-bedroom farmhouse, but now it is wrecked.’

Deborah Wassell, 47, a school secretary from Southampton, suffered ten years of damp problems after cavity insulation was installed in her three-bedroom semi. She had the insulation removed after furniture went mouldy and her son began to suffer asthma.

Yet she doesn’t blame the installers, saying: ‘This scheme was being pushed by the Government and energy firms.’